Doctors have been advising us for years to "use it or lose it": that is, to stay as intellectually active as possible into our waning years in order to avoid dementia. But the latest research shows that brain training comes at a price.

In a study of 1,157 men and women age 65 or older, researchers led by Dr. Robert Wilson at Rush University Medical Center in Chicago found that people who remained intellectually stimulated  by playing cards or other games, reading or visiting museums  were diagnosed with dementia later than those who were not as cognitively active. But once dementia set in, the group who participated in mentally stimulating activities experienced a much more rapid cognitive decline. Over the 12-year study, for each additional point they gained on a measure of cognitive activity, the intellectually stimulated group experienced a 52% greater decline in cognitive impairment, after being diagnosed with dementia.

"Brain activity is not stopping the underlying neurobiology of dementia, but for a while, it seems to be effective in delaying the additional appearance of symptoms," says Wilson. "But the benefit of delaying the initial symptoms comes at the cost of more rapid progression of dementia once it makes its appearance."

While brain exercises can help the brain continue to function despite the accumulating biological changes underlying dementia and Alzheimer's, at some point, says Wilson, the scales tip  that activity can no longer compensate for the growing volume of deteriorating alterations in the brain. "At that point, the patient is pretty much at the mercy of the pathology," he says. And that's why, once the symptoms of dementia become obvious, those who were able to push off their diagnosis are likely to be at a more advanced stage of disease.

The findings, published Wednesday in Neurology, should not discourage people from remaining cognitively active, says Dr. William Thies, chief medical officer of the Alzheimer's Association, and in fact raises interesting questions about how we as a society should approach age-related brain changes. Surveys consistently show that most of us would prefer to remain as functionally intact as possible and experience a short period of physical or mental disability before death. Gradual cognitive decline, which is the hallmark of Alzheimer's disease, is challenging for patients, their caregivers and society, as the health costs of chronic care continue to climb. But the current study suggests that more people may be able to telescope their mental decline into a shorter and more concentrated time period. "I think the results suggested by this paper are something that people would regard as positive," he says. "And this is the sort of study we really need if we are ever going to understand how to manage all aspects of dementia as a society."